function segments=contourenvelope(md,varargin)
%CONTOURENVELOPE - build a set of segments enveloping a contour .exp
%
%   Usage:
%      segments=contourenvelope(md,varargin)
%
%   Example:
%      segments=contourenvelope(md,'Stream.exp');
%      segments=contourenvelope(md,md.mask.elementonfloatingice)
%      segments=contourenvelope(md);

%some checks
if nargin>2,
	help contourenvelope
	error('contourenvelope error message: bad usage');
end
if nargin==2,
	flags=varargin{1};

	if ischar(flags),
		file=flags;
		file=varargin{1};
		if ~exist(file),
			error(['contourenvelope error message: file ' file ' not found']);
		end
		isfile=1;
	elseif isnumeric(flags),
		%do nothing for now
		isfile=0;
	else
		error('contourenvelope error message:  second argument should a file or an elements flag');
	end
end

%Now, build the connectivity tables for this mesh.
%Computing connectivity
if size(md.nodeconnectivity,1)~=md.numberofnodes,
	md.nodeconnectivity=NodeConnectivity(md.elements,md.numberofnodes);
end
if size(md.elementconnectivity,1)~=md.numberofelements,
	md.elementconnectivity=ElementConnectivity(md.elements,md.nodeconnectivity);
end

%get nodes inside profile
elementconnectivity=md.elementconnectivity;
if nargin==2,
	if isfile,
		%get flag list of elements and nodes inside the contour
		nodein=ContourToMesh(md.elements,md.x,md.y,file,'node',1);
		elemin=(sum(nodein(md.elements),2)==size(md.elements,2));
		%modify element connectivity
		elemout=find(~elemin);
		elementconnectivity(elemout,:)=0;
		elementconnectivity(find(ismember(elementconnectivity,elemout)))=0;
	else
		%get flag list of elements and nodes inside the contour
		nodein=zeros(md.numberofnodes,1); 
		elemin=zeros(md.numberofelements,1); 
		
		pos=find(flags); 
		elemin(pos)=1;
		nodein(md.elements(pos,:))=1;

		%modify element connectivity
		elemout=find(~elemin);
		elementconnectivity(elemout,:)=0;
		elementconnectivity(find(ismember(elementconnectivity,elemout)))=0;
	end
end

%Find element on boundary
%First: find elements on the boundary of the domain
flag=elementconnectivity;
if nargin==2,
	flag(find(flag))=elemin(flag(find(flag)));
end
elementonboundary=double(prod(flag,2)==0 & sum(flag,2)>0);

%Find segments on boundary
pos=find(elementonboundary);
num_segments=length(pos);
segments=zeros(num_segments,3);
count=1;

for i=1:num_segments,
	el1=pos(i);
	els2=elementconnectivity(el1,find(elementconnectivity(el1,:)));
	if length(els2)>1,
		flag=intersect(md.elements(els2(1),:),md.elements(els2(2),:));
		nods1=md.elements(el1,:);
		nods1(find(nods1==flag))=[];
		segments(count,:)=[nods1 el1];

		ord1=find(nods1(1)==md.elements(el1,:));
		ord2=find(nods1(2)==md.elements(el1,:));

		%swap segment nodes if necessary
		if ( (ord1==1 & ord2==2) | (ord1==2 & ord2==3) | (ord1==3 & ord2==1) ),
			temp=segments(count,1);
			segments(count,1)=segments(count,2);
			segments(count,2)=temp;
		end
		segments(count,1:2)=fliplr(segments(count,1:2));
		count=count+1;
	else
		nods1=md.elements(el1,:);
		flag=setdiff(nods1,md.elements(els2,:));
		for j=1:3,
			nods=nods1; nods(j)=[];
			if any(ismember(flag,nods)),
				segments(count,:)=[nods el1];
				ord1=find(nods(1)==md.elements(el1,:));
				ord2=find(nods(2)==md.elements(el1,:));
				if ( (ord1==1 & ord2==2) | (ord1==2 & ord2==3) | (ord1==3 & ord2==1) ),
					temp=segments(count,1);
					segments(count,1)=segments(count,2);
					segments(count,2)=temp;
				end
				segments(count,1:2)=fliplr(segments(count,1:2));
				count=count+1;
			end
		end
	end
end